Here's a failure pattern worth keeping in mind:
- Unbootable OS
- Attempts to access hard drive lock up or fail
- Hardware diagnostics show or imply bad sectors
- You image the raw partition to a good hard drive
- Data access and even OS bootability miraculously OK
What's happening here, is that effects from deeper abstraction layers are creating what appears to be unfixable problems in higher layers. What is counter-intuitive is that fixing the underlying layer can fix the upper layers too, i.e. that the state of these layers may not be irreparably botched by the lower-layer failure.
So don't give up hope, if you hit the first three items in the list above.